1. Field of the Invention
The present invention relates to thin-film magnetic heads in which shield layers are disposed on gap layers on both surfaces of a magnetic detecting element. In particular, the present invention relates to a thin-film magnetic head in which the insulation between the shield layers and the magnetic detecting element can be ensured and which has excellent heat dissipation performance and the shield layers having improved soft-magnetic characteristics.
2. Description of the Related Art
FIG. 8 is a fragmentary sectional view of a known thin-film magnetic head when viewed from a side opposing a recording medium.
The thin-film magnetic head has a lower shield layer 1 formed of, for example, a NiFe alloy and a lower gap layer 2 formed of, for example, Al2O3 on the lower shield layer 1.
As shown in FIG. 8, a magnetic detecting element 3 is formed on the lower gap layer 2. The magnetic detecting element 3 has a hard bias layer 5 and an electrode layer 6 which are formed on both sides of a multilayer film 4 in the track width direction.
The magnetic detecting element 3 is a spin-valve thin-film sensor in which the multilayer film 4 is composed of, for example, an antiferromagnetic layer, a pinned magnetic layer, a nonmagnetic conductive layer, and a free magnetic layer.
An upper gap layer 7 is formed of, for example, Al2O3 on the magnetic detecting element 3 and an upper shield layer 8 is formed of, for example, a NiFe alloy on the upper gap layer 7.
As the demand for a high recording density is increasing, the distance between the shield layers 1 and 8, that is, a gap length GI, becomes shorter to achieve a narrower gap. In order to achieve a narrow gap, the thicknesses of the lower gap layer 2 and the upper gap layer 2 need to be reduced.
For example, if the recording density increases to 70 Gbit/in2 from 40 Gbit/in2, the gap length G1 between the shield layers 1 and 8 must be reduced to about 600 xc3x85.
In this instance, if the thickness of the magnetic detecting element 3 is about 200 xc3x85 or more, the thicknesses of the lower gap layer 2 and the upper gap layer 7 must be about 200 xc3x85 or less.
However, if the lower gap layer 2 and the upper gap layer 7 have such a small thickness, they are liable to have pin holes, thus causing poor insulation between the magnetic detecting element 3 and the shield layers 1 and 8.
Poor insulation between the electrode layer 6 of the magnetic detecting element 3 and the upper shield layer 8 readily causes a short circuit between the electrode layer 6 and the upper shield layer 8, and this prevents an increase of reading output of the magnetic detecting element 3.
On the other hand, as the recording density is increased, the magnetic detecting element 3 more radiates heat. Accordingly, the heat must be conducted to the shield layers 1 and 8; hence, the gap layers 2 and 7 must have excellent heat dissipation performance.
Also, the shield layers 1 and 8 need to have a shielding function for absorbing an external magnetic field or noise to prevent the external magnetic field from affecting the magnetic detecting element 3. The shield layers 1 and 8, therefore, must be soft magnetic.
Accordingly, an object of the present invention is to provide a thin-film magnetic head in which the insulation performance between the shield layers and the magnetic detecting element can be ensured and which has an excellent heat dissipation performance and the shield layers having improved soft magnetic characteristics.
To this end, according to one aspect of the present invention, there is provided a thin-film magnetic head. The thin-film magnetic head includes a magnetic detecting element. Gap layers are disposed on both surfaces of the magnetic detecting element. Shield layers are each disposed on the corresponding gap layer. The magnetic detecting element side of at least one shield layer has a higher specific resistance than that of the other side.
For example, the shield layers each comprise a first shield sub-layer and a second shield sub-layer. The second shield-sub-layer is disposed on the corresponding gap layer and has a specific resistance higher than that of the first shield sub-layer.
The second shield sub-layers are electrically insulative due to the high specific resistance thereof. The electrical insulation of the thin-film magnetic head is, therefore, ensured by the gap layers and the second shield sub-layers. Thus, even if the thickness of the gap layers and the gap length become smaller, the insulation between the magnetic detecting element and the first shield sub-layers can be improved.
Also, by forming the second shield sub-layers with a thin film capable of ensuring electrical insulation, a heat dissipating thin-film magnetic head can be achieved. In this magnetic head, even if the temperature of the magnetic detecting element increases as the current density is higher according to increase of the recording density, heat can be released through the gap layers and the second shield sub-layers to the first shield sub-layers.
For example, the second shield sub-layers are formed of a magnetic material having a specific resistance higher than that of the first shield sub-layers. Hence, the second shield sub-layers which are formed of the magnetic material serve as shields as well as the first shield sub-layers.
In the present invention, therefore, the gap length G1 depends on the total thickness of the magnetic detecting element and the lower gap layers. Even though the gap length becomes smaller according to the demand for higher recording density, the second shield sub-layers can have a shielding function and improved electoral insulation performance.
Preferably, the first shield sub-layer and the second shield sub-layer are in contact with each other, thus generating a ferromagnetic bonding therebetween. Even if the second shield sub-layers have relatively worse soft magnetic properties such as magnetic permeability, the ferromagnetic bonding allows the soft magnetic first shield sub-layers to improve the soft magnetic characteristics of the second shield sub-layers. Thus, the second shield sub-layers can serve as adequate shield layers.
By forming the second shield sub-layers of a magnetic material having-a high specific resistance, a thin-film magnetic head can be achieved which have improved electoral insulation performance and an improved shielding function provided by both the first shield sub-layers and the second shield sub-layers.
The total thickness of the second shield sub-layer and the gap layer adjoining the second shield sub-layer may be in the range of 100 to 500 xc3x85. Thus, a thin-film magnetic head having improved electrical insulation performance and excellent heat dissipation performance can be achieved.
Preferably, the total thickness is in the range of 100 to 200 xc3x85. Thus, the present invention can be adapted event though the gap length is reduced to increase the recording density to 70 Gbit/in2 from 40 Gbit/in2.
Preferably, the thickness of the second shield sub-layer is in the range of 20 to 200 xc3x85.
More preferably, the thickness of the second shield sub-layer is in the range of 20 to 100 xc3x85.
Preferably, the thickness of the first shield sub-layer is in the range of 5xc3x97103 xc3x85 to 3 xcexcm. 
By setting the thicknesses of the first shield sub-layers and the second shield sub-layers in the above-described ranges, the electrical insulation performance and the heat dissipation performance can be improved.
Preferably, the second shield sub-layer comprises a magnetic oxide.
Specifically, the second shield sub-layer may comprise a Mnxe2x80x94Zn ferrite or a Nixe2x80x94Zn ferrite.
Since such a magnetic oxide has a high specific resistance, the second shield sub-layers can have improved electrical insulation performance while having improved soft magnetic characteristics to serve as shield layers in association with the first shield sub-layers due to the ferromagnetic bonding between the first shield sub-layers and the second shield sub-layers.
The second shield sub-layer may comprise a magnetic material represented by FeaMbOc. M is at least one element selected from the group consisting of Ti, Zr, Hf, Nb, Ta, Cr, Mo., Si, P, C, W, B, Al, Ga, Ge, and rare earth elements, and a, b, and c representing atomic ratios satisfy the relationships of 50xe2x89xa6axe2x89xa670, 5xe2x89xa6bxe2x89xa630, 10xe2x89xa6cxe2x89xa630, and a+b+c=100.
The second shield sub-layers may comprise a magnetic material represented by (Co1-gTg)xMyLzOw. T is Fe or Ni. M is at least one element selected from the group consisting of Ti, Zr, Hf, Nb, Ta, Cr, Mo, Si, P, C, W, B, Al, Ga, Ge, and rare earth elements; L is at least one element selected from the group consisting of Au, Ag, Cu, Ru, Rh, Os, Ir, Pt, and Pd; g representing an atomic ratio satisfies the relationship of 0xe2x89xa6gxe2x89xa60.7; y, z, and w representing atomic ratios satisfy the relationships of 3xe2x89xa6yxe2x89xa630, 0xe2x89xa6zxe2x89xa620, 7xe2x89xa6wxe2x89xa640, and 20xe2x89xa6y+z+wxe2x89xa660; and x represents the atomic ratio of the balance.
The second shield sub-layer may comprise a magnetic material represented by FedMeNf. M is at least one element selected from the group consisting of Ti, Zr, Hf, Nb, Ta, Cr, Mo, Si, P, C, W, B, Al, Ga, Ge, and rare earth elements, and d, e, and f representing atomic ratios satisfy the relationships of 60xe2x89xa6dxe2x89xa680, 10xe2x89xa6exe2x89xa615, 5 less than fxe2x89xa630, and d+e+f=100.
The magnetic materials described above have a high specific resistance, and can have a specific resistance of, for example, 104 xcexcxcexa9xc2x7cm can be achieved depending on the composition ratio of the materials. By using the magnetic materials for the second shield sub-layers, therefore, the electrical insulation performance can be improved. In addition, the ferromagnetic bonding between the first and second shield sub-layers allows the first shield sub-layers to improve the soft magnetic characteristics of the second shield sub-layers, and thus the second shield sub-layers can serve as shield layers in association with the first shield sub-layers. The materials for the second shield sub-layers are not limited to the above, but may be any magnetic material having a high specific resistance.